Wind tunnel testing of aeroelastic models often jeopardizes the model because aeroelastic instabilities such as flutter and divergence produce large, rapidly increasing model deformations that can lead to structural failure, thus destroying or severely damaging the model. It is common practice in aeroelastic model testing to take some precautions to minimize the risk of model damage when an aeroelastic instability is encountered. One method, called subcritical response technique, is to avoid encountering an instability by taking a series of measurements at conditions below the stability boundary and using these measurements in an analysis to predict the conditions at which the instability will occur. Although subcritical response methods show considerable promise, none has been developed that can be used with confidence in a variety of applications. In applications where subcritical techniques are applicable, it is usually necessary to reach at least one instability condition to verify the method.
Another means of reducing the risk of model damage is to conduct aeroelastic model studies in wind tunnels that have a means for rapidly reducing flow dynamic pressure. These means include such things as spoilers that are deployed in the tunnel diffuser to provide a choking effect and piping and valve arrangements that are used to short circuit flow between the low speed leg of the tunnel and the test section plenum. The spoiler is usually used in small tunnels and is usually very effective. The valve-piping system is more applicable to large tunnels and is not as effective as the spoiler. However, in both cases the wind tunnel must be equipped with the device before it can be used, requiring extensive modifications to the tunnel. Other methods of minimizing the risk of model damage include physical restraints to the model such as cables which are normally slack but become taut when the model deflection reaches a preset value. Although cable and other passive restraint methods are usually effective in minimizing model damage, their pressure does distort the flow over the model and does affect the dynamic characteristics of the model.
There is thus seen to be a need in the art for an improved aeroelastic instability stopper for wind tunnel models.
Accordingly, it is an object of the present invention to provide an improved apparatus for preventing large, potentially destructive deformations in wind tunnel models.
It is another object of the present invention to provide an instability stopper which is mechanically simple.
It is a further object of the present invention to provide an instability stopper which is capable of rapid actuation at any test condition.
It is yet another object of the present invention to provide an instability stopper which is adaptable to use in any wind tunnel.
It is also an object of the present invention to provide an instability stopper which is noninterfering with the dynamic characteristics of the model.
It is still another object of the present invention to provide an instability stopper which is noninterfering with the flow field around the model.